The present invention relates to treatment of semiconductor wafers with reactive gases formed from a plasma.
Copending, commonly assigned United States patent application Ser. No. 777,032, filed Sept. 17, 1985, U.S. Pat. No. 4,673,456 the disclosure of which is incorporated by reference herein, describes apparatus and methods for treating semiconductor wafers with reactive gases formed from plasmas. These gases are also referred to as "plasma afterglows" or "plasma products." As set forth in Ser. No. 777,032 application, a semiconductor wafer may be positioned within a reaction chamber and a gas containing oxygen and/or nitrous oxide downstream through a conduit to the reaction chamber. The conduit extends through a microwave reactor. In the reactor, microwave energy is applied to the gas passing through the conduit to convert the gas to a plasma as it passes through the plasma section of the conduit disposed in the microwave reactor. The plasma forms reactive gas species which pass downstream to the chamber containing the wafer and strips photoresist from the wafer. Reactive species created in substantially the same way can also be used in an anisotropic etching process also disclosed in Ser. No. 777,032 application. In the etching process, additional energy such as radio frequency energy is applied to the reactive species in the chamber containing the workpiece, so as to form ions and to bombard the workpiece with these ions. Radiant energy such as ultraviolet light typically is emitted by the plasma within the plasma section of the conduit. Semiconductor wafers and photoresists used thereon may be adversely affected by radiant energy. As described in Ser. No. 777,032 application, the conduit is provided with bends between the plasma section and the downstream end of the conduit. The bends in the path between the plasma section of the conduit and the workpiece-holding chamber preclude direct line of sight transmission of radiant energy from the plasma within the plasma section to the workpiece.
Other plasma treatment methods and apparatus wherein the gas is conveyed through a bent conduit from the plasma section to the wafer are disclosed in U.S. Pat. Nos. 3,837,856; 4,192,706; 4,123,663; 4,065,369; and 4,160,690. The conduits employed in a plasma treatment apparatus typically are formed from transparent or translucent materials such as fused silica, borosilicate glass, or alumina, as these materials resist reaction with the plasma and with the reactive species formed from the plasma. U.S. Pat. No. 4,304,983 discloses a treatment apparatus and method wherein the wafer is disposed in the central region of a chamber, the gas is converted to a plasma by an electrical discharge in a peripheral region of the chamber, and a series of baffles are provided between the central and peripheral regions of the chamber. These baffles likewise provide a path having at least one bend between the plasma generation section of the apparatus and the workpiece holding section so as to prevent direct, line of sight transmission of ultraviolet light from the plasma to the wafers.